Foam plastics manufacturing method and machine

ABSTRACT

Production of foamed materials in a horizontal machine, and said machine itself, reactants being fed to a conveyor at one end of the machine and foam produced being removed at the other end, wherein the foam is generated in an expansion chamber defined at its inlet by a closed reactant feed zone, at its outlet by a body of foam already expanded or partly expanded, and laterally and vertically by travelling webs, the webs giving a diverging cross section to the chamber.

FIELD OF INVENTION

[0001] The invention relates to a method and machine for makingpolyurethane and other plastics foams.

BACKGROUND

[0002] Essentially, foaming machines receive a mixture of reactants andprovide a path in which initial foaming of the reactant mix andsubsequent curing to form a self supporting polymer foam can take place.Blocks are then cut and matured.

[0003] In one form of machine the polymer foam is taken off vertically.Such machines are successful but require careful operation, not alwayseasy for those familiar with the usual horizontal machines, to ensurethat the foaming reaction takes place freely and that the foam developssufficient early strength for the spiked conveyors used to engage thefoam and carry it away.

[0004] In the other and by far the commoner form of machine, which isthe one the invention is concerned with, the polymer foam is taken awaygenerally horizontally. The machine is essentially a long channel, withreactants fed at one end to travelling webs of paper or plastics and thefoam taken off at the other. The machines inherently have a highproduction rate and are very large, production rates of 100 kg to 500 kgminute and lengths of over 100 metres being common. Capital costs arehigh, yet very often curing and handling the foam produced is a limitingfactor, or markets are modest, and plants are run only part of the day.A smaller, low-production machine would be desirable to make best use ofthe investment in a plant and produce foam for local markets rather thantransporting high-volume relatively low-value products long distances.

[0005] The high production rates are however inherent from the nature ofthe process in current machines. Prior to foaming, the reactants aredense compared to the initially-fluid foam they give rise to. Theconveyors taking the foam away, sloping forwards to ensure that foamdoes not simply escape from the back of the machine, have then to runfast enough to obviate the tendency of younger, high-density material tounderrun older, low density material in the forward direction of theconveyor. If materials did underrun, with lighter foam floating on topof denser material, finished foam of uneven properties would beproduced, but this is prevented by taking the older material away asfast as the younger material would otherwise run forward under it.

[0006] The problem is worsened by the limited steepness of profile thatstill-fluid foam can sustain. If the limit is exceeded the foam willslump back over younger, denser materials independent of underrunningtendencies as such, and to obviate slumping with a practical height ofblock, as well as the escape of reactants referred to above, the initialpart of the conveyor is invariably sloped downwards in the direction oftravel. This increases the tendency for underrunning and hence furtherincreases minimum conveyor speeds.

PRESENT PROPOSALS

[0007] To make a lower production rate, and hence smaller machine,possible, some change of principle is needed and we have seen that scopefor it lies in the early part of foam production in a horizontalmachine.

[0008] Horizontal is to be understood in a broad sense, as opposed tovertical, given that parts of the foam path can be inclined, indeed awhole machine while broadly horizontal could be designed for a site thatwas not level or for example to deliver foam product to a high or lowerfloor. However all existing horizontal machines operate with thereactants applied to an open, initially-inclined conveyor, sometimesdirectly, sometimes indirectly through a trough that feeds the conveyor,but with no confinement of materials during the initial part of thefoaming reaction. Bottom and side webs of paper or plastics film areused, but top webs where used are not applied in the early stages.

[0009] We have seen that this principle of open operation needs to beabandoned, the reactants instead being fed without exposure to theatmosphere and the foam being confined in a closed expansion chamber atleast while fluid enough to slump. Such confinement, in a process andmachine as defined in the claims herein, makes a low production ratepossible. Materials cannot run back and escape as there is nowhere torun to, nor can they slump, and with a suitable inclination of the partof the conveyor exposed to still-fluid foam, according to the nature ofthe foam being produced, they will not underrun. Laterally andvertically, that is at sides, bottom and top of the expansion chamber,they are confined by travelling webs and confinement and control istherefore complete.

[0010] A new machine will normally be built with no initial downwardslope of the part of the conveyor forming the base of the expansionchamber but, particularly where slumping rather than underrunning assuch is the tendency to be avoided, a downward (forward) slope of up to10°, preferably not more than 4°, may be acceptable. Existing machinesmay then be converted to the new form.

[0011] Preferably the conveyor when carrying still-fluid foam ishorizontal. Alternatively the tendency for underrunning is reduced orobviated at source by having at least part of the conveyor within theexpansion chamber sloping backward i.e. upward in the direction oftravel, provided the body of foam produced does not have to changedirection after it has ceased to be fluid. Typically, any slope of theconveyor will be for the initial part of the foam expansion only,exiting foam being for example at up to 20-30% of maximum expansion andin any case at most at 60% of maximum expansion so that a change ofdirection does not disrupt it. The slope may for example conveniently beup to 15° to the horizontal, but with a steeply inclined top web it canbe steeper, for example up to 30° to the horizontal.

[0012] In the expansion chamber, the walls diverge so that the crosssection increases in the direction of travel in a way matched to theexpansion rate of the foam, the reactant feed rate of course beingdetermined to keep the enclosure filled. The volume of the expansionenclosure and hence dwell time in it is at least sufficient to preventfoam that has exited the enclosure slumping backwards under its ownweight, if expansion is not being conducted wholly enclosed. Typically,the volume of the expansion enclosure is such that foam emerging from itis at least at 50% of its maximum expansion, and preferably 70% or morefor a standard flexible polyurethane foam, but for some foams e.g. MDIbased flexible high resilience foams or rigid polyurethane foams, whichdevelop gel-strength earlier, it can be down to 30%.

[0013] Production can then be at low rates, with foam coming to ahandleable stage over a short distance. Equally the invention isflexible. A low production rate machine may be installed and invariablyused as such. However there is no reason why a machine new as regardsits foam-production end should not be installed with a long conveyor andmovable block-cutting position. It can then be used at conventionalspeeds if certain grades of foam are regularly produced in greateramounts than others or occasional surges in demand are to be met, thenewly-facilitated low speeds being used otherwise.

FURTHER BACKGROUND

[0014] In considering the invention it is important to understand thebasic geometry of conventional foam slabstock processes, the principlesof foam flow-back (slumping) and foam under-running, and how theconveyor angle influences them. It is these factors, which limit thedegree by which the dimensions of a conventional machine can be reduced.

[0015] In the drawings, FIG. 1 shows a conventional foam slabstockprocess. Foam slabstock processes have traditionally used a downwardlyinclined conveyor (C), lined with paper or plastics film, onto which amixing head (A) continuously pours the liquid reactant mix (B). Thechemical reaction causes foam expansion up to the full rise position(E). The speed of the conveyor and the output rate of the liquidreactant mix determine the height of the foam block. The book “FlexiblePolyurethane Foams” published by Dow Plastics, second edition 1997, atpages 5.18 to 5.21, for example describes such a process.

[0016] The expanding foam is relatively fluid during most and especiallyin the early parts of its expansion. This means that there is a limit tothe height of a bank of expanding foam before it will flow (slump) underits own weight. It is necessary therefore to incline the conveyordownwards in the direction of production to prevent the expanding foam(D) flowing backwards. The higher the foam block, the more the conveyorneeds to be inclined. Typically an inclination angle of about 4 to 6degrees is used for a block height of up to 1.2 metres.

[0017] The inclination of the conveyor brings to the fore the potentialproblem of under-running. Under-running is where younger, higherdensity, lower viscosity liquid or partially expanded foam flowsunderneath older, lower density, higher viscosity material. The resultof under-running is densification and sometimes compression lines withinthe foam block, which render the foam product sub-standard.

[0018] In the drawings, FIG. 2A shows a geometric representation of thefoam rise profile of FIG. 1. The area (D) contained within the trianglefrom laydown (B) to full rise (F) represents the volume of foam whichhas been generated by the mass of foam chemicals dispensed within therise time of the foam. The angle of inclination of the conveyor is 6degrees. To reduce the dimensions of the machine, say to half those ofFIG. 2A, whilst still keeping the block height at 1.2 metres, the areaof the foam rise profile (D), that is to say volume of foam which hasbeen generated by the mass of foam chemicals dispensed within the risetime, would have to be halved. (The rise time is normally determined bythe chemical formulation and for this exercise should be consideredfixed).

[0019]FIG. 2B shows the geometric representation of the theoreticalhalf-size machine. The angle of the top of the foam profile cannot bemade steeper, or slumping will occur. The angle of the conveyor musttherefore be increased to 18 degrees to achieve the required shape offoam expansion profile. But such a steep conveyor will certainly resultin under-running. Halving the dimensions of the machine, whilst stillkeeping the same block height, is therefore not possible.

[0020] In conventional slabstock processes there is always arelationship between the conveyor angle and the height of foam block tobe produced at a given input of liquid reactant mix. If the conveyorangle is too small, liquid reactant mix or expanding foam will flowbackwards. If the angle is too great, under-running will occur. Both ofthese effects are undesirable and will cause defects in the finishedfoam product.

[0021] The book “Flexible Polyurethane Foams” published by Dow Plastics,second edition 1997, pages 5.22-5.23, describes a foam process (the‘Maxfoam’—trade mark—process) where the liquid reactant mix is allowedto pre-expand in a trough (F) such that the emerging material is atabout 5-10% of its final volume expansion before it flows at (G) ontothe conveyor. The first part of the conveyor is called a fall-plate (H)in this process. Because the foam already has a lower density and higherviscosity at this point, it is less prone to under-running and the angleof the fall-plate (H) can be greater (typically about 12 degrees averageinclination). This enables higher blocks to be produced for a givenoutput of liquid reactant mix and physical dimensions of the machine.There are however still limitations to how much the fall-plate can beinclined. If too great an inclination is used then under-running willstill occur.

THE INVENTION

[0022] The invention is set out in specific form in the claims but mayperhaps be most broadly stated as a process and machine for productionof foam where at least the first part of the expansion takes place in aclosed diverging expansion chamber, the chamber feeding a generallyhorizontal take off path for the foam produced and itself being fed withreactants from a closed feed zone.

[0023] Conveniently the base of the chamber is formed by a horizontalconveyor, or a conveyor that is upwardly inclined at least initially,but as already noted the conveyor can be downwardly inclined to suchdegree as does not give underrunning problems.

[0024] Only the early stages of expansion need necessarily take place inthe expansion chamber, as slumping is not a problem if a free upper faceof the foam is of limited height and of older, less-fluid foam.

[0025] In one embodiment the enclosure may conveniently be formed fromsurfaces consisting of the conveyor at the base, a pair of travellingsidewalls, and an upwardly inclined travelling topwall. Seals areprovided at the junctions of the four surfaces, and at the feed zone, toprevent leakage of liquid reactant mix or expanding foam.

[0026] Such a machine is well suited to making rectangular-sectionblock, the conveyor and travelling walls having or being formed of paperor plastics webs. However, other configurations are possible, forexample a single web may be guided to form a lay-flat tube withoverlapped edges which runs past a reactant feeder and is then guided toform a circular section enclosure to give round block for peeling.

[0027] In summary the invention can provide continuous horizontalproduction of foamed material wherein foam forming materials are fed ata controlled rate to a closed diverging expansion enclosure disposed atone end of a conveyor and foamed material is drawn away at the other endof the conveyor at a corresponding rate; at least the initial part ofthe foam expansion takes place in the enclosure bounded laterally andvertically by moving sheet materials, the materials travelling with thefoaming material in paths diverging in at least one plane; and theenclosure is defined at its inlet by a closed feed zone sealed againstsaid moving sheet materials and at its exit end by foam which hasalready partly or fully expanded.

PRIOR PROPOSALS

[0028] There are several publications which bear a superficialresemblance to the present proposals, but which on inspection are foundto miss the essential novel features of the invention. For example FIG.4 shows a modified representation of the drawing from U.S. Pat. No.3,984,195 (del Carpio, assigned to Planiblock), which describes afoaming process, wherein a top paper or plastics film (1) is applied tothe top of the expanding foam (D), forming a type of divergingenclosure. Rollers (J) or plates (K) are applied to the top surface ofthe paper or film to shape the foam. It is to be noted however that theliquid reactant mix (B) is freely poured onto the conveyor (C) beforethe top paper or film (1) is applied, there being no seal provided atthe point of introduction (L) of the liquid reactant mix to thedivergent enclosure. The arrangement, as drawn in del Carpio'sspecification, would thus not work, as the bottom conveyor (C) ishorizontal and expanding foam would flow backwards out of the machine.In practice, Planiblock run the process as drawn in FIG. 4, with theconveyor at a downwardly inclined angle of about 4-6 degrees, to preventsuch flow-back.

[0029] Similar processes are described in U.S. Pat. No. 4,150,075 (WilliSchmitzer et al), U.S. Pat. No. 5,665,286 (Sulzbach et al), U.S. Pat.No. 4,128,611 (Kolakowski et al) and U.S. Pat. No. 4,097,210(Romanillos). A top paper or plastics film is applied to the top of theexpanding foam to form a type of diverging expansion zone. All theseprocesses however pour the liquid reactant mix freely onto the bottomconveyor before the top paper or film is applied and therefore wouldgive the same problem of flow-back if the bottom conveyor were notinclined downwards in the direction of production.

[0030] Further published proposals are:

[0031] EPA 0 645 226 concerning unconstrained expansion of CO₂— frothedfoam in a chamber or froth cavity that is not closed and has a strongforward slope at its base.

[0032] EPA 0 000 058 concerning, again, unconstrained expansion of foamin an unsealed enclosure with strongly forward sloping base.

DETAILS OF THE INVENTION

[0033] The bottom of the expansion enclosure is conveniently defined bya paper or plastics film sheet or web, which is continuously fed ontothe main bottom conveyor.

[0034] The top of the enclosure may similarly be defined by a secondpaper or plastics web, constrained by a top inclined conveyor driven atabout the same speed as the foam. Restraining surfaces may be used, suchas a fixed board coated with a low friction surface or a perforatedmetal plate, through which air is blown to reduce friction between thesheet and the plate. The length of the top inclined conveyor, board orplate will depend on the fluidity of the foam. Foams which are fluid fora greater part of their expansion will require a greater length ofconstrained surface.

[0035] The sides of the expansion enclosure may likewise be defined bythird and fourth papers or plastics webs, constrained by side walls.

[0036] The feed end of the expansion enclosure is defined by a closedfeed trough or channel, which is fitted with seals which contact thewebs as they pass it, and prevent leakage of foam. A suitable seal hasbeen found to be a flexible plastic lip which is bonded to the peripheryof the feed trough or channel at the point where the webs pass it. Theseflexible plastic lips are positioned such that they make intimatecontact with the webs, thus forming a foam-tight seal.

[0037] The out-going end of the expansion enclosure is defined byexpanded or partly expanded foam already produced.

[0038] The foam-forming chemicals may be fed in several ways:

[0039] i) A liquid mix may be fed directly into the expansion enclosurethrough a narrow channel whose width is the same as the expansionenclosure and which is sealed against the four webs.

[0040] ii) The liquid mix may be fed into a trough of volume sufficientto allow some pre-expansion of the foam before it enters the expansionenclosure. The trough is fitted with seals to prevent leakage where thewebs come in.

[0041] iii) The foam forming chemicals may be supplied as a froth, forexample a froth produced by dissolving gas, such as carbon dioxide underpressure and then releasing the pressure under controlled conditions.Such froth may readily be fed into the expansion zone, with seals toprevent leakage.

[0042] The height of the foam block will be related to the density ofthe fully expanded foam and can be varied by adjusting input rate of thefoam-forming mix and/or the conveyor speed.

[0043] The width of the foam block may be fixed in the case of a simplelow-budget machine. However provision may be made for it to be changedby adjusting pre-set positions of the sidewalls and by utilisingdifferent widths of in-feed channels or troughs.

[0044] An arrangement is also possible where the width of the block maybe changed during running, “on-the-fly”. In such a case, the mainsidewalls, after the expansion enclosure, are continuously adjustable inor out, to change the width of the block. The sections of the sidewallswhich form part of the expansion enclosure are pivoted at the in-feedend and can swing in or out at the expansion enclosure exit, to coincidewith the settings of the main sidewalls.

[0045] Cylindrical block, suitable for peeling, can be produced. Theexpansion enclosure may be essentially as described, but at a pointwhere the expanding foam is still fluid, it passes through suitablyshaped formers which cause the block formed to be of a circular crosssection. The main conveyor in such an instance may consist of a flexiblebelt, which can be formed into a semi-circular shape to support thecylindrical foam block.

THE DRAWINGS

[0046] A list of the drawings, which as to FIGS. 1 to 4 have alreadybeen discussed, is:

[0047]FIG. 1. Conventional horizontal machine

[0048]FIGS. 2A, 2B. Schematic (2A) of foam rise in the machine of FIG.1, with theoretical steepened and shortened initial conveyor section(2B)

[0049]FIG. 3. Schematic of known trough and fall plate machine

[0050]FIG. 4. Representation of a known top-paper machine (del Carpio),as used in practice

[0051]FIG. 5. Side view of a machine according to the invention

[0052]FIG. 5A View as in FIG. 5 but with shorter top conveyor

[0053]FIG. 6. Top view of the machine of FIG. 5

[0054]FIG. 7. Detail of in-feed seal

[0055]FIG. 8. Partial side view of machine with initial backwards(upward) conveyor orientation

[0056]FIG. 9. Partial top view of variable block width machine

[0057]FIG. 10. Partial side view of modified machine with outgassingprovision

[0058]FIG. 11. Partial side view of further modified machine

[0059]FIG. 12. Top view corresponding to FIG. 11

[0060]FIG. 13. Section from FIG. 12, showing block configuration

[0061] FIGS. 14 to 16 Views of a machine for forming ‘round block’ forpeeling

[0062] The drawings FIGS. 5 and 6 show, respectively, a side view and atop view of a machine according to the invention, in basic form. Theexpansion enclosure (8) is defined by a main lower conveyor (6), anupper, inclined conveyor (7) with adjustable or interchangeable edgesupport plates (7A) to allow for adjustment of block width, and two sidewalls (11), which seal against them. Main side walls (12) defining theblock width adjoin the walls (11). Papers or plastics films (2, 4, 16and 18) are fed in from unwind rolls (3, 5, 17 and 19), past an in-feedtrough (1) to line the inside surfaces of the expansion enclosure (8).They move with the conveyor and against the inner surfaces of the sidewalls, separating them from the outer surfaces of the foam block. Thetrough, which is drawn spaced from the papers/films for clarity, is infact sealed against them. The papers or films may be removed from thefoam block and rewound onto rolls (20A, 20B, 21A and 21B) before thefoam reaches a cut-off knife (13). Alternatively, some or all of thepapers or films may be left adhered to the surface of the foam block.

[0063] The main conveyor (6) determines the speed of the foam block. Theupper inclined conveyor (7) is driven at the same speed, or slightlyfaster than the main conveyor (6).

[0064] The foam-forming chemical mix is delivered from a mixing headinto the feed trough (1). The volume of the trough determines the timedelay before the chemical mix or partially expanded foam enters theexpansion enclosure (8). The early part of the foam expansion takesplace inside the expansion enclosure (8), and the remaining expansion upto the full-rise position (9) continues outside the expansion enclosure.

[0065] The time from full-rise (9) to the cut-off knife (13) isdetermined by the speed and length of the conveyor (6). The cut block(14) is removed by a take-off conveyor (15).

[0066]FIG. 5A shows a modification to the machine in FIG. 5 and FIG. 6,where the top, inclined conveyor (7) is shorter. Whereas in FIG. 5 andFIG. 6 the foam exiting from the expansion zone (8) is expanded toapproximately 80-90% of the final volume expansion, in FIG. 5A it isabout 50-60% of the final volume expansion. Such a situation isconsistent with a foam type where the froth viscosity develops morerapidly and the expanding foam becomes self-supporting in a shortertime. This is typical of a rigid polyurethane foam and some types ofhigh-resilience flexible foams.

[0067]FIG. 7 shows a close-up view of the sealing arrangement of thetrough (1) against the papers or plastics films (2 and 4) as they runpast it, onto the conveyor and side-wall inner surfaces. Flexible lipseals (22) are fixed to the edges of the trough so that they contact thepapers or films and prevent leakage.

[0068]FIG. 8 shows a modification to the machine in FIG. 5 where thebottom conveyor (6) is made to incline backwards (i.e. upwards) at thefeed end of the expansion enclosure (8) by the introduction ofadditional rollers (23 and 24). This is advantageous in the case of foamformulations that are particularly fluid during the early stages of foamexpansion.

[0069]FIG. 9 shows a further modification of the machine in FIG. 5 wherethe main side walls (12) can be moved in or out to change block width,and sections of the side walls (11) fit between the main conveyor (6)and the upper inclined conveyor (7). They are pivoted at a point closeto the fixed width in-feed trough (1) and are thus able to swing in andout to match the position of the main side walls (12) when they aremoved to make a change in block width. Such an arrangement allows widthchanges to be made whilst running, or “on-the-fly”, without changing thesize of the infeed trough.

[0070]FIG. 10 shows a further modification to the machine in FIG. 5where the top paper or film is temporarily lifted off the upper surfaceof the block, to release gases evolved at the full-rise position, byroller (25) and then re-applied by roller (26).

[0071]FIG. 11 and FIG. 12 show side view and top view respectively of afurther modification to the machine in FIG. 5. The upper inclinedconveyor (7) and the edge support plates (7A) have been shortened in thedirection of production and the areas which have been removed arereplaced by a board or metal plate (27) having a low-friction surface.

[0072] The board (27) is narrower than the distance between theexpansion enclosure sidewalls (11), as shown in FIG. 12. The upper edgesof the expanding foam within the part of the expansion chamber definedby the conveyor (7) and the edge support plates (7A) are constrained.When the expanding foam reaches the narrower board (27) the upper edgesare now unconstrained and the foam is able to expand upwards higher atthe edges than in the centre.

[0073]FIG. 13 shows a cross-section through the process at Section A-Aof FIG. 12. The board or metal palate (27) restrains the foam expansionover the main part of the block, but at the top edges (28) the foam hasexpanded more, creating slightly raised top corners on the finished foamblock. This results in a foam block that can be trimmed to give a fullyrectangular cross-section, with minimal cutting waste.

[0074]FIG. 14 and FIG. 15 show a general three-dimensional view and sideview respectively of a modified machine, designed to produce cylindricalfoam blocks for peeling. The chemical reactants are fed into theexpansion zone (8) through the in-feed trough (1), which is sealedagainst the two moving films (2) and (4). The edges of the two films (2)and (4) are bonded together (29) as they contact each other at the sidesof the in-feed trough (1), so forming an expansion zone (8) in the formof a continuous flexible sleeve.

[0075] The shape of the upper part of the expansion zone is determinedby the top, inclined conveyor (7). The initial part of the bottom, mainconveyor (6) is flat and determines the shape of the lower part of theexpansion zone.

[0076] The bottom, main conveyor is flexible in the transverse directionand is progressively shaped from flat to semicircular cross-section by aseries of rollers (30).

[0077] Curved steel shaping elements (31) are positioned at the top ofthe expanding foam contained in the flexible film sleeve. These help tomaintain the circular cross-section of the foam block.

[0078] Cylindrical blocks of the required length are cut off by theknife (13).

[0079]FIG. 16 shows progressive cross-sections through the expansionzone (8) at points A-D indicated in FIG. 14. At point A thecross-section is virtually flat and follows the shape of the in-feedtrough (1). At points B, through to D, the cross-section increases inarea as the shape becomes gradually more circular.

PROCESS EXAMPLES Example 1

[0080] A machine according to FIG. 5 was used, having the followingdimensions: Main conveyor total length 12 metres Main conveyor width 2.4metres Upper inclined conveyor length 2.5 metres Upper inclined conveyorwidth 2.2 metres (conveyor +  adjustable edge-plates) Inclination ofupper conveyor 26° to horizontal Distance between sidewalls 2.2 metresIn-feed trough (1) volume 35 litres

[0081] Chemical formulation, related to parts by weight per hundred ofpolyol: Polyol - Voranol CP3322 (Dow Chemicals) 100.00 Toluenediisocyanate - T80 (Bayer) 53.24 Water 4.20 Silicone BF2370(Goldschmidt) 1.00 Amine catalyst - Niax Al (Crompton) 0.05 Aminecatalyst - Dabco 33LV (Air Products) 0.15 Tin catalyst - stannousoctoate 0.20

[0082] These materials are in themselves conventionally used formanufacture of flexible polyether polyurethane foam slabstock and thus:—

[0083] Voronol CP3322 is a poly (propylene-ethylene) triol, molecularweight 3500

[0084] T80 is 80:20 Toluene diisocyanate

[0085] Tegostab B 2370 is a proprietary silicone surfactant suitable forflexible polyether slabstock production

[0086] Niax A1 and Dabco 33LV are proprietary tertiary amine catalystssuitable for flexible polyurethane foam slabstock production.

[0087] Running Conditions: Polyol input 70 kg/mm Total chemical input110 kg/mm Conveyor speed 1.8 metres/minute Full-rise distance (frommouth of in-feed trough) 2.5 metres Block height (hot) 1.2 metres Blockwidth (hot) 2.2 metres Time from in-feed to cut-off 6.7 minutes

[0088] A foam block of good quality was produced, having a sample-piecedensity of 22.5 kg/m³.

Example 2

[0089] A machine according to FIG. 5 was used, having the followingdimensions: Main conveyor total length 12 metres Main conveyor width 2.4metres Upper inclined conveyor length 2.5 metres Upper inclined conveyorwidth 2.2 metres (conveyor  + adjustable edge plates Inclination ofupper conveyor 22° to horizontal Distance between sidewalls 2.2 metresIn-feed trough (1) volume 40 litres

[0090] Chemical formulation, related to parts by weight per hundred ofpolyol: Polyol - Voralux HN 360 (Dow Chemicals) 100.00 Toluenediisocyanate - T80 (Bayer) 31.80 Water 2.20 Silicone Tegostab B-8681(Goldscbmidt) 0.90 Amine catalyst - Niax Al (Crompton) 0.12 Aminecatalyst - Dabco 33LV 0.24 (Air Products) Cross-linker - diethanolamine0.70 Liquid FR (fire retardant) additive - 5.00 trichloropropylphospateTin catalyst - dibutyltin dilaurate 0.25

[0091] These materials are again in themselves conventionally used formanufacture of flexible high resilience polyurethane foam slabstock andthus:—

[0092] Voralux HN 360 is an ethylene oxide tipped poly(propylene-ethylene) triol, molecular weight 5000, suitable formanufacture of high-resilience slabstock

[0093] T80 is 80:20 Toluene diisocyanate

[0094] Tegostab B-8681 is a proprietary silicone surfactant suitable forhigh-resilience foam slabstock production

[0095] Niax A1 and Dabco 33LV are proprietary tertiary amine catalystssuitable for flexible polyurethane foam slabstock production.

[0096] Running Conditions Polyol input 110 kg/min Total chemical input150 kg/min Conveyor speed 1.5 metres/minute Full-rise distance 2.8metres (from mouth of in-feed trough) Block height (hot) 1.1 metresBlock width (hot) 2.2 metres Time from in-feed to cut-off 8.0 minutes

[0097] A high resilience foam block of good quality was produced, havinga sample-piece density of 42 kg/m³

Example 3

[0098] A machine with block width adjustment “on the fly”, according toFIG. 9 was used, having the following dimensions: Main conveyor totallength 12 metres Main conveyor width 2.4 metres Upper inclined conveyorlength 2.5 metres Upper inclined conveyor width 2.3 metres Inclinationof upper conveyor 26° to horizontal Distance between sidewallsadjustable 1.8 to 2.3 metres In-feed trough volume 25 litres

[0099] Chemical formulation, related to parts by weight per hundred ofpolyol: Polyol - Voranol CP3322 100.00 (Dow Chemicals) Toluenediisocyanate - T80 (Bayer) 56.94 Water 4.60 Methylene chloride blowingagent 5.00 Silicone BF 2370 (Goldschmidt) 1.40 Amine catalyst - Niax A1(Crompton) 0.05 Amine catalyst - Dabco 33LV 0.15 (Air Products) Tincatalyst - stannous octoate 0.30

[0100] Running Conditions (at Start): Polyol input 43 kg/min Totalchemical input 73 kg/min Conveyor speed 1.7 metres/minute Full-risedistance (from mouth of (in-feed trough) 2.5 metres Block height (hot)1.2 metres Block width (hot) 1.9 metres Time from in-feed to cut-off 7.0minutes

[0101] The initial distance between the sidewalls (12) was set at 1.9metres. After running for 30 minutes, the distance between the sidewalls(12) was increased slowly, over a period of 30 seconds to 2.1 metres,the hinged sidewalls (11) associated with the expansion enclosure movingsimultaneously so that their ends remained in line with the start of themain sidewalls. As the sidewalls were moved outwards, the chemicaloutput was increased to 48 kg/min polyol (82 kg/min total).

[0102] Samples of foam taken from the blocks of 1.9 m and 2.1 metreswidth both had a sample piece density of 18 kg/m³. The length of thefoam block of varying width associated with the change in width was only1 metre.

ADVANTAGES

[0103] Overall, the invention gives a new slabstock process which allows(but is not necessarily restricted to) running at lower output thanconventional processes, and which will produce full-sized foam blocksand run a full range of foam types and grades.

[0104] The invention can be applied to any foam slabstock process whichproduces foamed plastics from an expandable liquid reactant mixture, forexample rigid polyurethane foam, phenolic foam, epoxy foam, siliconerubber foam.

[0105] The new machine has a low capital cost and is suited to the needsof the smaller manufacturer, who may require 2000 tonnes or less offinished foam annually. Large conventional machines need to makerelatively long production runs to be efficient but a low-output machineproduces efficiently on shorter runs. Rates of chemical emissions can bereduced, making treatment of those emissions easier The machine occupiesa small floor area, thereby requiring a smaller factory. Also, the floorarea necessary for curing the blocks, before using or transporting themis reduced.

[0106] Particularly, the lower rate of chemical metering results in aproportional decrease in the quantity of fumes emitted by the process.This has the advantage that any fume-scrubbing equipment required bylocal authorities for limiting atmospheric emissions can be smaller insize and of reduced cost.

[0107] Another application in which the invention is valuable isvariable pressure foaming.

[0108] It is a well-known principle that if the ambient air pressureunder which foaming is conducted changes the foam density changesaccordingly. Reduced air pressure results in proportionally lower foamdensity. In high altitude locations (e.g. Mexico City) it is found thatfoam densities are significantly lower than at locations at sea level,when running the same formulation.

[0109] Many processes have been described where the foaming process isenclosed within a pressure/vacuum chamber so that the air pressure canbe artificially controlled, thereby providing a means of controlling thefoam density. These processes need a complicated system of transferconveyors and air-locks to enable cut blocks to be removed to normalatmospheric pressure, whilst maintaining the foaming process at apressure different from atmospheric. The overall size of the machine,including transfer conveyors and air-lock, is related to conveyor speed.When a conventional foaming process, for example ‘Maxfoam’ (trade mark)with conveyor speed of about 5 metre/minute, is used, this results in along total process which is very expensive. If the basic foam machinecan be shortened and the conveyor speed reduced, say to one third thatof the conventional process, a significantly smaller pressure controlledplant can be envisaged. This significantly lowers costs and is what thepresent invention provides.

[0110] A similar saving is made in forced cooling processes, wherevolumes of air are drawn though the hot foam block, a short time afterfoaming, to cool it to such a temperature where it can be handled.

[0111] The polyurethane foam reaction is strongly exothermic. The maincontribution to the exotherm is the water-isocyanate reaction.Consequently, greater quantities of water and isocyanate in the chemicalmixture result in hotter foam blocks.

[0112] It is generally considered that 165° C. is a safe maximumexotherm temperature and foam producers will generally limit water andisocyanate levels to keep within this limit.

[0113] The cellular structure of foam makes it a relatively good heatinsulator. This means that freshly produced hot blocks of foam take along time to cool down to ambient temperature before they can be used.Typically, this cooling time is 6 to 12 hours.

[0114] Several processes have been described, where air is drawn throughthe hot foam block, shortly after production, by standing it on asuction table or conveyor. This cooling process typically takes about 10to 15 minutes, the time being determined by the porosity of the foamblock. If the cooling process is to be continuous and in-line with thefoaming process, the conveyor speed must be the same. For a standardMaxfoam machine this will be about 5 metres/minute. The cooling processtherefore has to be 59-75 metres long to provide the required coolingtime.

[0115] A shorter foam machine, running at a slower conveyor speed, ofsay 2 metres/minute, as described in this invention, will require acooling conveyor only 20-30 metres long to achieve the same coolingtime.

1. Production of foamed slabstock in a horizontal machine, reactantsbeing fed through a reactant feed zone to a conveyor at one end of themachine and foam produced being removed at the other end, wherein inorder to support and constrain the rise profile of a body of expandingfoam while in the fluid state: the reactant feed zone is closed, with noexposure of reactants to the atmosphere, the foam is generated in anexpansion chamber closed at its inlet by the reactant feed zone, at itsoutlet by a body of foam already expanded or partly-expanded, at topsides and bottom by travelling webs, the chamber has a cross-sectionarea that progressively increases in the direction of production, thebase of the expansion chamber is not inclined forwards or is so inclinedby no more than 10 degrees to the horizontal.
 2. Production of foamaccording to claim 1, the base of the expansion chamber being inclinedforwards at no more than 4° to the horizontal.
 3. Production of foamaccording to claim 1 or 2, wherein the foam continues to expand afterexiting the expansion chamber, having at exiting reached at least 30%,and optionally at least 50%, of its full-rise volume and a consistencyat which its rise profile can be maintained without slumping. 4.Production of foam according to any preceding claim, wherein at least aninitial section of the conveyor and thus at least part of the base ofthe expansion chamber slopes backwards in the production direction at upto 30° to the horizontal, optionally at up to 15° to the horizontal, thefoam leaving this section having reached at most 60%, optionally no morethan 20 to 30%, of its full-rise volume, whereby the body of foamproduced does not have to change direction after it has ceased to befluid.
 5. Production of foam according to any preceding claim, whereinthe feed zone is the exit from a trough sealed against the webs anditself fed with reactants, expansion of the foam optionally starting inthe trough.
 6. Production of foam according to any preceding claim,wherein the reactants are initially in the form of a froth produced byrelease of pressure on a dissolved gas.
 7. Production of foam accordingto any preceding claim, wherein movable sidewalls allow thecross-machine width of the expansion chamber and hence the block widthproduced to be varied.
 8. Production of foam according to any precedingclaim, wherein the webs are guided to a circular cross section while thefoam is still fluid, to give round block for peeling.
 9. Production offoam according to any preceding claim, wherein the top face of theexpanding foam is fully constrained centrally but only by a web at thesides, whereby the foam can displace the web to rise at the sides abovethe general plane of the top face, obviating the formation of roundedblock shoulders and minimising trimming waste in forming square-corneredblock.
 10. Production of foam according to any preceding claim, whereina top web is retained on the block produced but is lifted temporarily ator around full rise to allow outgassing.
 11. Production of foamaccording to any preceding claim, wherein the foam machine is in anenclosure wherein the pressure can be maintained at a value above orbelow atmospheric pressure to influence the final foam density, theenclosure being provided with appropriate air lock to enable removal offoam blocks to atmosphere without significantly influencing the pressureinside the enclosure.
 12. Production of foam according to any precedingclaim, wherein the hot foam blocks produced are conveyed through aforced-cooling station where air is drawn though the foam blocks to coolthem.
 13. A horizontal machine for the production of foamed materials,wherein in use reactants are fed through a reactant feed zone to aconveyor at one end of the machine and foam produced is removed at theother end, and in order to support and constrain the rise profile of abody of expanding foam while in the fluid state: the reactant feed zoneis closed, with no exposure of reactants to the atmosphere, the foam isgenerated in an expansion chamber closed at its inlet by the reactantfeed zone, at its outlet by a body of foam already expanded orpartly-expanded, at top sides and bottom by travelling webs, the chamberhas a cross-section area that progressively increases in the directionof production, the base of the expansion chamber is not inclinedforwards or is so inclined by no more than 10 degrees, to thehorizontal.
 14. Machine according to claim 13, the base of the expansionchamber being inclined forwards at no more than 4° to the horizontal.15. Machine according to claim 13 or 14, wherein the expansion chamberis dimensioned to allow foam to continue to expand after exiting theexpansion chamber, having at exiting reached at least 30%, optionally atleast 50% of its full-rise volume and a consistency at which its riseprofile can be maintained without slumping.
 16. Machine according to anyone of claims 13 onwards, wherein at least an initial section of theconveyor and thus at least part of the base of the expansion chamberslopes backwards in the production direction at up to 30° to thehorizontal, optionally at up to 15° to the horizontal, allowing foamleaving this section to reach up to 60%, optionally no more than 20 to30%, of its full-rise volume, whereby the body of foam produced does nothave to change direction after it has ceased to be fluid.
 17. Machineaccording to any one of claims 13 onwards, wherein the feed zone is theexit from a trough sealed against the webs and having means to be itselffed with reactants, expansion of the foam optionally starting in thetrough. 18 Machine according any one of claims 13 onwards, having meansto feed reactants initially in the form of a froth produced by releaseof pressure on a dissolved gas.
 19. Machine according any one of claims13 onwards, wherein movable sidewalls allow the cross-machine width ofthe expansion chamber and hence the block width produced to be varied.20. Machine, according to any one of claims 13 onwards, wherein the websare guided to a circular cross section while the foam is still fluid, togive round block for peeling.
 21. Machine, according to any one ofclaims 13 onwards, wherein the top face of the expanding foam is fullyconstrained centrally but only by a web at the sides, whereby the foamcan displace the web to rise at the sides above the general plane of thetop face, obviating the formation of rounded block shoulders andminimising trimming waste in forming square-cornered block.
 22. Machineaccording to any one of claims 13 onwards, wherein a top web is retainedon the block produced but is lifted temporarily at or around full riseto allow outgassing.
 23. Machine, according to any one of claims 13onwards, in an enclosure wherein the pressure can be maintained at avalue above or below atmospheric pressure to influence the final foamdensity, the enclosure being provided with appropriate air lock toenable removal of foam blocks to atmosphere without significantlyinfluencing the pressure inside the enclosure.
 24. Machine, according toany one of claims 13 onwards, wherein the foam blocks produced areconveyed through a forced-cooling station where air is drawn through thefoam blocks to cool them.